Microwave surgery electronic device

ABSTRACT

Disclosed is an electrode device for microwave surgery which is provided with a marker securely fixed to the central electrode, which marker can provide a magnetic susceptibility artifact of a uniform size and shape free of fluctuation among electrode devices. The electrode device comprise a central conductor body, a tubular insulator body which covers the central conductor body except its distal end, a tubular external electrode which covers the tubular insulator body except its distal end part, and a central electrode which covers the distal end part of the central conductor body. The central conductor body, the insulator body, the external electrode and the central electrode are made of a nonmagnetic material, and a cylindrical member made of a magnetic material is fit around the distal end part of the central conductor body. At least one projection is defined on the lateral face of the central conductor body at the distal side of the cylindrical member, and the cylindrical member engages with the projection in the distal direction.

TECHNICAL FIELD

The present invention relates to an electrode device suited for use inmicrowave surgery performed under MRI (magnetic resonance imaging)monitoring. More specifically, the present invention relates to anelectrode device to be used in a microwave surgery instrument, which,using microwave, performs coagulation of a biotissue, arrestshemorrhages and carries out partial excision, which electrode device cancause to generate an artifact that is uniform in size and shape free offluctuation among electrode devices, on a MRI monitor screen displayingthe site that is undergoing an operation.

BACKGROUND ART

Microwave surgery is a technique to selectively coagulate affected partof the body, arrest hemorrhages and perform partial excision utilizingdielectric heat generated in a tissue of the body by a localizedmicrowave electromagnetic field created between electrodes which areinserted in the affected part of the body and between which a microwaveof a predetermined frequency is emitted. As to microwave surgery of adeep site of the body, percutaneous microwave coagulation therapy (PMCT)and laparoscopic microwave coagulation therapy (LMCT) are widelyapplied. A recent development of an open-type MRI apparatus has enabledmicrowave surgery to be conducted under real-time observation of theaffected site utilizing such a MRI apparatus. Microwave electrodedevices for this purpose are made of a material substantially inert tothe magnetic field created by the MRI apparatus, i.e., a nonmagneticmaterial so that they do not hinder monitoring of the affected site.Thus, it has been difficult to detect inserted microwave electrodedevices on a MRI monitor screen.

The difficulty in detecting a microwave electrode device on the MRImonitor screen, however, causes inconvenience for the surgeon that he orshe can not identify, on the MRI monitor screen, the position of themicrowave electrode inserted in the body relative to the affected site.To address this problem, a method has been conceived in which a markerof magnetic material is attached near the distal end of the electrodedevice to induce a magnetic susceptibility artifact (hereinafterreferred to simply as an “artifact”), which is an area observed blackaround the marker on the MRI monitor screen, thereby making it easier toroughly identify, on the MRI monitor screen, the position of thecoagulating or cauterizing electrode device in the body. For this, it isproposed to place solder, metal plating such as titanium coating, and amounted ring member as markers (Japanese Patent Application PublicationNo. H11-267133).

However, with solder or metal plating, it is difficult to control theamount of the marker to be placed on microwave electrode devices, and,therefore, fluctuation in marker amount among microwave electrodedevices is hard to eliminate. Fluctuation among electrode devices in theamount of the placed solder or titanium coat causes fluctuation in thesize of the artifact. As a general rule, electrode devices for microwavesurgery are disposed of after a single use of them for safetyrequirements such as prevention of transmission, surgeons are forced touse new electrodes in each operation. A MRI monitoring screen displaysonly a specific cross section of the body. Consequently, the size of theartifact is greatest when a marker is positioned on this specific crosssection, and the artifact reduces its size or eliminates when the markerdeviates from the specific cross section as a function of the distancefrom it. If there is fluctuation in the size of generated artifact amongelectrode devices, a surgeon, who manipulates an electrode devicerelying on the position and the size of the artifact, must identify inevery operation the maximal diameter of the artifact induced by theelectrode device used while using the very electrode device and thenreflect this to his manipulation. This causes a great deal ofinconvenience and impedes achieving the uniformity of manipulation.

In addition, in order to keep coagulated tissues from adhering to themicrowave electrode device being used, a fluorocarbon resin is coated onthe electrode device. As the baking temperature for this (about 390° C.)is what solder (melting at about 200° C.) cannot stand, use of solder asa marker would cause a trouble in application of fluorocarbon resincoating. Furthermore, when water is lost from tissues being cauterizedin an operation, the electrodes could reach high temperatures, and this,due to the melting of the solder, could lead to risks of leaking andfalling of the solder on the lesion.

In the case where a ring member is to be mounted as a marker, there is aproblem of how to securely fix the member to prevent it from looseningor falling. That is, in microwave surgery now, needle-like devices areused because of year-to-year request for thinner, needle-like electrodedevices. Thus, where an electrode with small diameter is inserted in aring-shaped marker member, it would become necessary to securely fix themarker member onto the electrode. A screw or other components cannot beapplied, however, due to the small diameter of the electrode. As forwelding, arc welding cannot be applied, for it would not only cause anuncontrollable extra artifact due to added welding materials but alsolead to reduction in the strength of the electrode due to residualstress. Although application of spot welding could evade the problems ofan extra artifact and reduction in the strength, it is difficult tosecurely fix the ring-shaped member by spot welding alone. Otherwise,spot welding applied in excess also could lead to reduction in thestrength of the electrode due to remaining stress. Moreover, foreasiness of an operation, a marker is to be mounted preferably onto thecentral conductor body at the tip of the electrode device. However,because of the narrow diameter of the central conductor body, it is muchmore difficult to securely fix a marker ring onto the central conductorbody. And further, when the tip of the electrode device is burnt andbonded to a cauterized tissue, it is necessary to manipulate theelectrode device to detach its tip from the biotissue, in the process ofwhich stress is concentrated on the tip of the electrode device. In casethe marker ring is not securely fixed onto the central conductor body,it could lead to an event that the marker detaches due to the stress andfalls together with the central electrode covering the marker.

As electrode device, as a general rule, is to be disposed of after eachoperation, means for securely fixing the marker must be simple andapplicable at low costs so as not to be a factor that could cause aprice rise of the device.

DISCLOSURE OF INVENTION

Against the background mentioned above, the objective of the presentinvention is to provide, by a simple and therefore low-cost method, anelectrode device for microwave surgery, which can be used in microwavesurgery performed under monitoring on a MRI apparatus and which isprovided with a marker which can give an artifact that is uniform insize and shape free of fluctuation among electrode devices and issecurely fixed onto the central conductor body.

Through suitable defining of the shape of a marker member together withfinding of a well-suited way of binding a central conductor body and themarker member, the present inventors succeeded in creating an electrodedevice for microwave surgery which achieves the above-mentionedobjective.

Thus, the present invention provides an electrode device for microwavesurgery comprising a central conductor body, a tubular insulator bodywhich covers the central conductor body except distal end part of thecentral conductor body, a tubular external electrode which covers thetubular insulator body except distal end part of the tubular insulatorbody, and a central electrode which covers the distal end part of thecentral conductor body, wherein

-   -   any of the central conductor body, the tubular insulator body,        the tubular external electrode and the central electrode is made        of a nonmagnetic material, and a cylindrical member made of a        magnetic material is fit around the distal end part of the        central conductor body,    -   at least one projection is defined on the lateral face of the        central conductor body on the distal side of the cylindrical        member, and    -   the cylindrical member engages with the projection in the distal        direction.

According to the present invention, a cylindrical member, which is amarker of a magnetic material readily and definitely formed to have auniform mass and a uniform shape, can be incorporated, in a securelyfixed form, in a microwave electrode device made of nonmagneticmaterials by enabling the cylindrical member to engage with theprojection of the central conductor body. Thus, if the cylindricalmember receives a strong tensile force in the distal direction, therewill be no risk of falling off of the marker or the central electrodecovering it, for any displacement of the cylindrical member in thedistal direction is prohibited by the engagement. In addition, thepresent invention gives an artifact that is uniform in size and shapeand free of fluctuation among electrode devices in an operation undermonitoring on a MRI apparatus. Furthermore, as the marker can besecurely fixed in a simple manner, the present invention can bepracticed at a low cost.

The present invention further provides an electrode device for microwavesurgery described above, wherein the engagement of the cylindricalmember with the projection is made by meshing, with the projection, ofat least one notch defined in the cylindrical member at the distal sidethereof.

The present invention further provides an electrode device for microwavesurgery, wherein a pair of projections are defined on the opposite sideof the lateral face of the central conductor body, and the engagement ofthe cylindrical member with the pair of projections is made by meshingof the pair of projections with a pair of notches defined in thecylindrical member on the distal side thereof at positions facing theprojections.

The present invention further provides any one of the above-describedelectrode devices for microwave surgery, wherein the cylindrical memberdefines an opening in the intermediate area of the lateral face thereof.

The present invention further provides any one of the electrode devicesfor microwave surgery described above, wherein the cylindrical memberincludes an overhanging portion formed by extending part of thecircumference on the distal or proximal side of the cylindrical memberin the longitudinal direction.

The present invention further provides any one of the above-describedelectrode devices for microwave surgery, wherein the cylindrical memberfurther defines a slit extending in the longitudinal direction throughthe both ends thereof.

The present invention further provides an electrode device for microwavesurgery, wherein a pair of projections are defined on the opposite sidesof the lateral face of the central conductor body, wherein thecylindrical member includes an overhanging portion formed by extendingpart of the circumference on the distal side of the cylindrical memberin the longitudinal direction, the overhanging portion unrotatablyengaging at each of the both lateral edges with each of the pair ofprojections, wherein the front edge of the cylindrical member engages atthe foot of the overhanging portion with the projections in a mannerwhere displacement of the front edge in the distal direction isprohibited.

Still more, the present invention provides any one of theabove-described electrode devices for microwave surgery, wherein thefront edge of the cylindrical member includes notches facing the pair ofprojections at the foot of the overhang portion, and the projectionsengage with the notches.

The present invention still further provides any one of theabove-described electrode devices for microwave surgery, wherein spotwelding is made between the cylindrical member and the central conductorbody.

The present invention further provides any one of the above-describedelectrode devices for microwave surgery, wherein the cylindrical memberis made of stainless steel.

The present invention further provides any one of the above-describedelectrode devices for microwave surgery, wherein the mass of thecylindrical member is 1-10 mg.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a general view of an electrode device for microwave surgery.

FIG. 2 is an enlarged view of a distal region of the electrode device ofExample 1 including a partial cross sectional view.

FIG. 3 is a perspective view of the marker member of Example 1 coupledto the central conductor body.

FIG. 4 is a perspective view of the central conductor body of Example 1.

FIG. 5 is a perspective view of the marker member of Example 1.

FIG. 6 is a perspective view of the marker member of Example 2.

FIG. 7 is a perspective view of the marker member of Example 2 coupledto the central conductor body.

FIG. 8 is a perspective view of the marker member of Example 3.

FIG. 9 is a perspective view of the marker member of Example 4.

FIG. 10 is a perspective view of the marker member of Example 5.

FIG. 11 is a perspective view of the marker member of Example 5 coupledto the central conductor body.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, the term a “magnetic material” means such amaterial that has a level of magnetic susceptibility enough to induce anartifact in images being monitored by MRI. Examples of it includestainless steel (SUS), nickel alloys (cupronickel), copper-nickel-zincalloys (brass+nickel (10-20%), cobalt-chromium alloys, etc.

In the present invention, the term a “nonmagnetic material” means amaterial that has such a limited magnetic susceptibility that can notinduce an artifact in MRI images. Examples of it includes brass(cupper+tin), phosphor bronze (cupper+tin+phosphor), copper, zinc, gold,silver alloys, etc.

Under a constant imaging condition, the size of an artifact correlatesto the material and mass of the cylindrical member used as a marker. Forexample, in the case of stainless steel (SUS 304), 1-10 mg, or morepreferably 3-10 mg of it can induce an artifact of a moderate size inMRI monitoring images. However, the material and the mass of the markermay be determined as desired in accordance with the size of the artifactrequested. In any case, the present invention enables to securely fix amarker of a precise amount of mass to provide electrode devices thatgives uniformly sized artifacts that are free of device-to-devicefluctuation.

In the present invention, an additional marker member may also beattached at another position, e.g., in the intermediate part of thecentral conductor body. In this case, the plural artifacts induced bythe plural marker members make it easier to see the relative positionsand orientation of the affected site and the electrode device.

EXAMPLES

The present invention will be described in further detail below withreference to examples. It is not intended, however, that the presentinvention be limited by the examples. In the figures, each referencenumber indicates: 1=monopolar electrode device for microwave surgery,2=coaxial cable connector, 3=external electrode, 4=insulator body,5=central electrode, 6=central conductor body, 7=marker member,8=projection, 9=overhanging portion, 12=notch, 17=marker member,19=overhanging portion, 22=notch, 27=marker member, 32=notch,33=opening, 37=marker member, 42=notch, 44=slit, 47=marker member.

Example 1

FIG. 1 illustrates a general view of a needle-like monopolar electrodedevice 1 for microwave surgery of this example. In the electrode device1, numeral 2 indicates a coaxial cable connector, numeral 3 acylindrical external electrode, numeral 4 a tubular insulator bodyextending through the external electrode 3, and numeral 5 a centralelectrode. A coating of fluorocarbon resin is applied to cover theentirety of external electrode 3, insulator body 4 and central electrode5. The distance from the root of the external electrode to the tip ofthe central electrode is 252 mm, the external diameter of the externalelectrode and the central electrode 1.6 mm, the length of the centralelectrode 10 mm, and the length of the exposed part of the insulatorbody 6 mm.

FIG. 2 illustrates an enlarged view of a distal area of the electrodedevice 1 shown in FIG. 1 including a partial cross sectional view. Inthe figure, the external electrode 3 is made of brass plated with gold,the tubular insulator body 4 of a fluorocarbon resin PTFE (Teflon(trademark)), and the central electrode 5 of phosphor bronze plated withgold. The central electrode 5, which defines a conical sharp tip at itsdistal end for piercing tissues, has a generally cylindrical cavity,into proximal part of which the distal end part of the insulator body 4is fit. In the cavity of the central electrode 5 is inserted the distalend part of the central conductor body 6 which extends through theinsulator body 4 and protrudes from the distal end thereof. The centralconductor body 6 is made of phosphor bronze plated with silver. On thecentral conductor body 6 is fixed, in a manner mentioned later, acylindrical marker member 7 of stainless steel (SUS 304) for inducing anartifact in MRI monitoring images. The central electrode 5 which coversthe marker member 7 is securely fixed on it by swaging from outside atfrontal and rear positions of the marker member 7. Thus, the centralconductor body 6, the marker member 7 and the central electrode 5 arecombined, and the central electrode 5 is electrically integrated withthe central conductor body 6 via the marker member 7.

FIGS. 3-5 illustrates the manner of secure fixation of the centralconductor body 6 and the marker member 7 within the central electrode 5.As seen in the figures, there are provided a pair of oppositely directedprojections 8 on the lateral face of the central conductor body 6 nearthe distal end thereof. The height of the projections 8 is designed sothat the tops of the projections 8 are roughly flush with the outersurface of the marker member 7. Although the projections 8 may be formedby any way as desired in this example, they are formed by pinching thecentral electrode between dies to allow plastic deformation to occur.

The marker member 7 (1 mm in outside diameter, 3 mm in length, 6 mg inmass) includes a cylindrical portion on its proximal side through whichthe central conductor body 6 is to be passed and a overhanging portion 9which is formed by extending part of the circumference of thecylindrical portion forward in the longitudinal direction. The shape anddimensions of the marker member 7 including the overhanging portion 9,and those of the central conductor body 6 including the projections 8,are designed so that, when the marker member 7 is slid forward on thecentral conductor body 6 up to the position illustrated in FIG. 3, theupper surfaces of the both lateral edges of the overhanging portion 9 ofthe marker member 7 come into contact with the lower surfaces of thepair of projections 8 on the central conductor body 6, and that the rearedges of the pair of projections 8 come into contact with the frontedges of the cylindrical portion of the marker member 7. Thus, in theposition illustrated in FIG. 3, the marker member 7 is blocked, by itsengagement with the pair of projections 8, from shifting forward alongthe central conductor body 6 and from rotating around the axis relativeto the central conductor body 6. Further, spot welding is performedbetween the marker member 7 and the central conductor body 6, therebyblocking backward sliding of the marker member 7 relative to the centralconductor body 6 and electrically integrating them. The spot welding maybe made by applying spot welding electrodes onto the exposed surface ofthe central conductor body 6 over the overhanging portion 9 of themarker member 7 and any surface of the marker member 7, e.g., the lowersurface of the overhanging portion 9. This manner of secure fixation ofthe marker member 7 onto the central conductor body 6 provides such afirm binding between the central conductor body 6 and the marker member7 that is sufficient to bear external forces that can be applied betweenthe central conductor body 6 and the marker member 7 in a variety ofstages during microwave surgery, inter alia, twisting and tensileexternal forces that otherwise could cause troubles.

Testing Under MRI Monitoring:

Ten grams of agar were added to 500 ml of physiological saline,completely dissolved by heating and stirring, then poured into a moldand allowed to cool to give an agar block for use in place of anaffected site.

The above-obtained agar block was placed in an open-type MRI apparatus(SIGMA SP/i, 0.5 tesla, manufactured by General Electric Company). UnderMRI monitoring using the gradient echo method, the electrode device formicrowave surgery of the present example was inserted along the agarblock's cross section being monitored by MRI. On the monitor screen, anartifact with a clear boundary seen as a nearly circular black hollow ofabout 10 mm in diameter was clearly observed to move, in a homogenousgray cross section of the agar block that emerged in a black background,as the electrode device was inserted.

Example 2

FIG. 6 illustrates the shape of the marker member 17 used in thisexample, and FIG. 7 the marker member 17 as secured onto the centralconductor body 6. Except the shape of the marker member 17, thecomponents of this example are identical to those of Example 1, and spotwelding also is performed as in Example 1. The marker member 17 includesa cylindrical portion on its proximal side, through which the centralconductor body 6 is to be passed, and an overhanging portion 19 which isformed by extending part of the circumference of the cylindrical portionin the longitudinal direction, and defines a pair of notches 12 in thefront edge of the cylindrical portion at the foot of the overhangingportion 9. The shape and the dimensions of the notches 12, as seen inFIG. 7, are designed so as to allow engagement with the projections 8 onthe central conductor body 6. In this example, the notches 12 engagewith the projections 8 on the central conductor body 6 and each of theprojections 8 contacts, on its upper and lower surfaces, with the upperand lower surfaces of one of the notches 12 (and with an upper surfaceof either of the lateral edges of the overhanging portion 19), therebyachieving securer fixation against twisting.

Example 3

FIG. 8 illustrates the shape of the marker member 27 used in thisexample. Except the shape of the marker member, this example isidentical to Example 1. The marker member 27 is generally cylindricaland defines notches 22 for receiving and engaging with the correspondingpart of the pair of projections 8 provided on the central conductor body6. Spot welding is performed by applying electrodes to an exposedsurface of the central conductor body 6 and any surface of the markermember. This example achieves as firm a fixation as Example 2, for thepair of projections 8 on the central conductor body 6 are fit in thenotches 22 of the marker member 27.

Example 4

FIG. 9 illustrates the shape of the marker member 37 used in thisexample. Except the shape of the marker member, this example isidentical to Example 1. The marker member 37 in this example, as inExample 3, is generally cylindrical and defines notches 32 for receivingand engaging with the corresponding part of the pair of projections 8provided on the central conductor body 6, and further defines in itslateral face an opening 33 which is not present in the marker member 27in Example 3. When the marker member 37 is placed on the centralconductor body 6 at a predetermined position, the opening provides aconvenient surface for applying one of the welding electrodes forcarrying out spot welding, by exposing part of the central conductorbody 6 under the marker member 37. The other of the electrodes may beapplied to, e.g., the lower face of the marker member 37.

Example 5

FIG. 10 illustrates the shape of the marker member 47 used in thisexample, and FIG. 11 the marker member 47 as attached onto the centralconductor body 6. Except for the shape of the marker member 47, thecomponents of this example are identical to those of Example 1. Themarker member 47, as the marker member 27 in Example 3, is generallycylindrical and defines notches 42 for receiving and engaging with thecorresponding part of the pair of projections 8 provided on the centralconductor body 6, and further defines in its lateral face a slit 44extending in the longitudinal direction through the both ends, which isnot present in the marker member 27 in Example 3. The slit 44 provides,in the gap defined by it, an exposed surface of the central conductorbody 6, which may be utilized as desired to apply a welding electrode tothe central conductor body 6 in carrying out spot welding of the markermember 47 and the central conductor body 6. The width of the slit 44 ofthe marker member 47 will not be expanded by external forces conceivableto the electrode device, for the marker member 47 fixed onto the centralconductor body 6 is squeezed by the internal surface of the centralelectrode 5 by swaging the central electrode 5, which closely covers themarker member 47, from outside at frontal and rear positions of themarker member 47. Therefore, the presence of the slit 44 does not affectthe secure fixation of the marker member 47 and the central conductorbody 6, and the marker member in this example is thus fixed as firmly asin other examples.

INDUSTRIAL APPLICABILITY

According to the present invention, an electrode device for microwavesurgery is provided which can be used in microwave surgery performedunder monitoring on a MRI apparatus and which comprises a securely fixedmarker which provides an artifact of a uniform size and shape free offluctuation among electrode devices.

1. An electrode device for microwave surgery comprising a centralconductor body, a tubular insulator body which covers the centralconductor body except distal end part of the central conductor body, atubular external electrode which covers the tubular insulator bodyexcept distal end part of the tubular insulator body, and a centralelectrode which covers the distal end part of the central conductorbody, wherein any of the central conductor body, the tubular insulatorbody, the tubular external electrode and the central electrode is madeof a nonmagnetic material, and a cylindrical member made of a magneticmaterial is fit around the distal end part of the central conductorbody, at least one projection is defined on the lateral face of thecentral conductor body on the distal side of the cylindrical member, andthe cylindrical member engages with the projection in the distaldirection.
 2. The electrode device for microwave surgery of claim 1,wherein the engagement of the cylindrical member with the projection ismade by meshing, with the projection, of at least one notch defined inthe cylindrical member at the distal side thereof.
 3. The electrodedevice for microwave surgery of claim 1, wherein a pair of projectionsare defined on the opposite side of the lateral face of the centralconductor body, and the engagement of the cylindrical member with thepair of projections is made by meshing of the pair of projections with apair of notches defined in the cylindrical member on the distal sidethereof at positions facing the projections.
 4. The electrode device formicrowave surgery of claim 1, wherein an opening is defined in theintermediate area of the lateral face of the cylindrical member.
 5. Theelectrode device for microwave surgery of claim 1, wherein thecylindrical member further defines a slit extending in the longitudinaldirection through the both ends thereof.
 6. The electrode device formicrowave surgery of claim 1, wherein the cylindrical member includes anoverhanging portion formed by extending part of the circumference on thedistal or proximal side of the cylindrical member in the longitudinaldirection.
 7. The electrode device for microwave surgery of claim 1,wherein a pair of projections are defined on the opposite sides of thelateral face of the central conductor body, wherein the cylindricalmember includes an overhanging portion formed by extending part of thecircumference on the distal side of the cylindrical member in thelongitudinal direction, the overhanging portion unrotatably engaging ateach of the both lateral edges with each of the pair of projections,wherein the front edge of the cylindrical member engages at the foot ofthe overhanging portion with the projections in a manner wheredisplacement of the front edge in the distal direction is prohibited. 8.The electrode device for microwave surgery of claim 7, wherein the frontedge of the cylindrical member includes notches facing the pair ofprojections at the foot of the overhang portion, and the projectionsengage with the notches.
 9. The electrode device for microwave surgeryof claim 1, wherein spot welding is made between the cylindrical memberand the central conductor body.
 10. The electrode device for microwavesurgery of claim 1, wherein the cylindrical member is made of stainlesssteel.
 11. The electrode device for microwave surgery of claim 1,wherein the mass of the cylindrical member is 1-10 mg.